Naturally Occurring Radioactive Material and Technically Enhanced NORM

Naturally Occurring Radioactive Material in Oil & Gas Operations – Mike Arthur – Penn State

Most human activity exposes the body to radiation in one form or another whether from the sun shining overhead or from elements within earth. This is referred to as naturally occurring radioactive material or NORM. Lifestyle and occupation can change one’s exposure rates to NORM. Also, industrial activities like mining and processing can concentrate naturally occurring radioactive material in the environment. We call this technically enhanced NORM or TENORM. It is critical for personnel in the petroleum industry to understand how they might be exposed to TENORM and how to mitigate the risks.

The likelihood of exposure to non-routine radiation sources in oil fields and refineries depends on both the region and source of hydrocarbons. For example, the relatively geologically young oil sources and reservoirs in California are not highly radioactive in comparison to the much older rocks and reservoirs of the Appalachian basin. There are different types of radiation and different ways of being exposed to it. The two most common elements composing NORM from geological sources are uranium, primarily uranium 238, and radium, typically, radium 226.

Radiogenic isotopes of some other common elements such as thorium, potassium and lead also emit measurable amounts of radiation. Radiation emitted by these elements occurs in the form of alpha particles, beta particles or gamma rays depending on the isotope. Because they are particles, alpha and beta radiation is easily stopped by thin layers of plastic or metal. Gamma rays, on the other hand, are high-intensity waves of electromagnetic radiation. These waves easily pass through many materials. Gamma radiation is considered an external hazard to living tissue and requires containment with thick layers of lead.

Appropriate protective clothing and respirators can provide protection from alpha and beta particles, but it would not prevent exposure to gamma rays. Alpha and beta decay is almost always accompanied by gamma decay. Gamma rays are electromagnetic waves with very high frequencies and energy, so protective clothing can minimize total radiation exposure, but it won’t block more harmful gamma radiation. Hydrocarbon production can concentrate NORM, as large quantities of materials from beneath earth’s surface are collected, transported and stored. This means workers can be exposed to radiation in a variety of ways and at different stages of hydrocarbon production. Radioactive uranium and thorium may be found in formations above and within hydrocarbon reservoirs and may be found in well cuttings brought to the surface. This is particularly problematic in unconventional shale wells with long horizontals that penetrate hydrocarbon bearing shales with high uranium and radium contents.

Fluids are another area of risk. Uranium and thorium are generally sparsely soluble in fluids, but radium mobilizes with produced water and hydrocarbons and can precipitate as a radioactive mineral scale in well casing, pipelines and tanks. Radium can be filtered from solution using clay cakes or precipitated as a component of carbonate minerals. Radioactive gas can contaminate the air. Radon, a gas, migrates with natural gas, but because of its short half life of 3.8 days is generally less of a problem. Radon can, however, build up in enclosed spaces.

Exposure to radiation from TENORM has two kinds of effects, acute and delayed. High levels of radiation immediately cause certain blood chemistry changes, nausea, fatigue, cataracts and a skin effect resembling sun burn. Long-term exposure to uranium has been linked to cancer, and kidney and liver damage. Radium mimics calcium in the body, increasing the risk of bone and blood cancers. The Environmental Protection Agency mandates maximum contaminate levels for uranium and radium in drinking water. However, these levels differ for waste water and landfill disposal of sludges and other solid wastes. The allowable levels are much higher for waste water and sludges taken to landfills. That’s why appropriate safety procedures must be followed when handling these materials.

For oil field workers or inspectors, the most common exposure to radiation will be through pipes, tanks, logging tools, produced water and cuttings. The key to avoiding radiation exposure is to know when it’s there. This is done through monitoring. There are several ways to monitor radiation levels. Probing near the surface with an uncompensated Geiger-Muller tube will measure alpha and beta particles released by decaying elements. Gamma ray screening can be accomplished with a sodium iodide base detector. Although gamma rays have no charge and thus no detector is directly sensitive to them, gamma rays do interact with matter and produce charged particles, typically electrons.

The electrons in a sodium iodide crystal scintillate to produce an amount of light. These light pulses are converted to electrical pulses in a photo multiplier tube. Although these detectors sometimes overestimate the gamma dose rates, these crystals are particularly useful because charged particles produce an amount of light directly proportional to their energy. A compensated Geiger-Muller tube provides a slower measurement but a more accurate indication of present radiation. This gas-filled tube scintillates when a charged particle enters the tube. This type of counter measures total radiation and does not distinguish particles types. In recent years, technology has advanced to the point that workers can wear a small device that measures total radiation levels. Personal radiation detectors or PRDs are relatively inexpensive and typically accurate to plus or minus 15%. Workers who may be exposed to radiation should be outfitted with these devices.

Petroleum production carries with it many safety risks. That’s why personnel must be educated, procedures must be followed and appropriate technology must be employed to ensure a safe working environment.